The present invention relates to a device and a method for holding, transporting and releasing crustacea juveniles, in particular lobster juveniles.
The object of the invention is to provide a device which enables the holding, transportation and release of crustacea juveniles, in particular lobster juveniles, in such a way that the juveniles are protected against predators until the juveniles have reached a stage, in which they have settled to the bottom and, on the bottom, instinctively leave the device which is formed by two main devices, which will be referred to below as the housing section and the emigration device.
Larvae that hatch from egg-bearing lobster with released eggs, live free-floating in the water until they have gone through three ecdyses and reached the fourth stage. Depending on the temperature of the water, this process varies from between two to six week. As the larvae are pelagic and even from birth are relatively big, they are, until in the fourth stage when they are about to settle to the bottom, a very easy prey for fish and other organisms hunting for food. Research results have proved that the survival rate until settling is about 0.5% for lobster juveniles born from egg-bearing lobster on the sea bed.
Because of this relatively low percentage of survival and because of the fact that, in their pelagic state, lobster juveniles can easily be carried away by sea currents from their hatching area, there is a wish to protect the lobster larvae against predators while in their pelagic stage and in the following stages until, after having been released onto oceanic feeding grounds, they instinctively leave the device, so that the survival percentage and recapture rate will increase considerably relative to what is achieved in normal release of lobster juveniles. Further, it is a wish that a relatively large number of lobster juveniles may be released in one single operation, in which the transport and the release operation itself can be carried out by preferably one person by means of relatively simple means, so that the operation becomes cost effective.
There are known a great number of devices for rearing and feeding lobster juveniles. From NO B 164271, U.S. Pat. No. 4,559,902, U.S. Pat. No. 4,198,924, U.S. Pat. No. 3,889,639 and U.S. Pat. No. 4,036,176 are known different facilities for rearing crustacea which are kept on discs or baskets in a vessel. Feed is supplied to the vessel or to the individual disc or basket by means of different types of feed supplying devices.
The prior art mentioned above presents several good solutions related to the rearing of, among other things, lobster which is in the pelagic stage, in which the lobster juveniles are protected against predators and lobster relatives. However, none of the above-mentioned documents shows or proposes any devices for transport and safe transfer of juveniles to free oceanic feeding grounds on the sea bed. Even though the juveniles are protected from hatching to release, the lobster juveniles are in a highly critical stage when being transferred from the rearing facility to the sea. It is common to carry out this release by releasing individuals into the sea from a boat. With this method relatively many individuals are eaten by predators before reaching the bottom of the sea. To reduce this critical stage, experiments have been done to carry the lobster juveniles from the boat to the sea bed by releasing the juveniles through a pipe or hose extending down to the bottom. This is, like the above-mentioned method, relatively time-consuming work and may entail that the juveniles are released at times which are not necessarily the best for the juveniles to stand a good chance of survival.
A further drawback of rearing juveniles individually, is that the juveniles are not trained for a life together with lobster relatives, which may result in loss of juveniles after the juveniles have been released on oceanic feeding grounds, because the juveniles have not developed any natural survival instincts.
From U.S. Pat. No. 3,449,421 and U.S. Pat. No. 4,279,218 are known devices which provide protection in the form of a cage for the individual lobster which remains in a rearing facility its entire lifetime.
Keeping lobster in a cage until it is ready for consumption is resource-demanding with respect to both technical devices and feeding and caring.
The invention has as its object to remedy, or at least reduce, one or more drawbacks of the prior art.
The object is realized through features which are specified in the description below and in the following Claims.